[ggt-devel] Re: adding GetColumn to ggt Matrix?

[Ben S. <bs...@ga...>]

While it could be considered an unneeded function because you can achieve
the same functionality on your own, I have often wanted the ability to get
a column from a matrix as vector - especially when getting the forward
vector for entities or doing billboarding. It's a relatively simple
function that will bloat the API but not the user's code unless they use
it. I figure that GMTL is hard enough for most people to grok because of
the templates that anything we can do to help them use it and like it is
good.

I guess if Allen agrees with you and doesn't want it in the library I'll
concede and just send Eric the patch rather than commit it.

cheers,
-Ben

>
>
> I'm not sure it was an ambiguity, rather it was an effort not to bloat the
> code with unneeded functions.
>
> for example, you can easily write your own GetColumn using the element
> accessor operator (  mat[row][col]  ).
>
> I see it as unneeded, but I'll defer the descision to allen or ben since I
> don't feel too strongly about it.
>
> kevin
>
>
> On Mon, 22 Sep 2003, Eric Maslowski wrote:
>
>> Ben said he was going to take a look into adding GetColumn() routine to
>> the
>> library to simplify this ambiguity. Thanks for the response.
>>
>> cheers
>>
>> E.
>>
>> At 15:13 09/22/2003 -0500, you wrote:
>>
>> >mats are column ordered, so that helps.  you should be able to index
>> one
>> >element and dereference it to get the column.
>> >
>> >I think (float*)&mat.mData[0] would be the first column, which if you
>> init
>> >a Vec with it:
>> >
>> >gmtl::Vec4f col;
>> >col.set( (float*)&mat.mData[0] );
>> >
>> >
>> >second column (example):
>> >
>> >    col.set( (float*)&mat(0,1) );
>> >
>> >
>> >4th column (translation component):
>> >
>> >    col.set( (float*)&mat[0][3] );
>> >
>> >
>> >
>> >-kevin
>> >
>> >
>> >
>> >On Mon, 22 Sep 2003, Eric Maslowski wrote:
>> >
>> > > How this is the right list: What is the recommended method for
>> grabbing an
>> > > entire column?
>> > >
>> > > Can't seem to find a general GetColumn() routine in the Matrix
>> definition.
>> > > I can't seem to even grab the components and throw them in a vector
>> when
>> > > the Matrix44f is a pointer.
>> > >
>> > > Matrix44f* mat = entity->GetTransform(); // GetTransform() returns
>> > Matrix44f*
>> > > Vec3f out_vec(mat[2][0],mat[2][1],mat[2][2]);
>> > >
>> > > yields:
>> > >
>> > > error C2664: 'gmtl::Vec<DATA_TYPE,SIZE>::Vec(const DATA_TYPE &,const
>> > > DATA_TYPE &,const DATA_TYPE &)' : cannot convert parameter 1 from
>> > > 'gmtl::Matrix<DATA_TYPE,ROWS,COLS>::RowAccessor *' to 'const float
>> &'
>> > >
>> > > Any help would be greatly appreciated.
>> > >
>> > > cheers
>> > >
>> > > E.
>> > >
>> > >
>> > >
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>> >
>> >--
>> >*--*---*---*----*-----*------*------*-----*----*---*---*--*
>> >Kevin Meinert                         /_/
>> >home - http://www.vrsource.org/~kevin           \        /
>> >music - http://www.subatomicglue.com           \/  __    \/
>> >                                                    \__
>> >                                             \_\
>>
>>
>
> --
> *--*---*---*----*-----*------*------*-----*----*---*---*--*
> Kevin Meinert                         /_/
> home - http://www.vrsource.org/~kevin           \        /
> music - http://www.subatomicglue.com           \/  __    \/
>                                                    \__
>                                             \_\
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>